Shifts in the physical environment in the Pacific Arctic and implications for ecological timing and conditions

Abstract The northern Bering Sea and Chukchi Sea represent the gateway from the Pacific to the Arctic. This contiguous marine system encompasses one of the largest continental shelves in the world and serves as the sole point of connection between the North Pacific and Arctic Ocean. This region has unique attributes and complex dynamics, driven by the convergence of distinct water masses, dynamic currents, advection between Pacific and Arctic systems, and important latitudinal gradients relevant to stratification and water mass structure, water temperature, and seasonal ice cover. Many processes and interactions in the region appear to be changing with important implications for both hydrography and ecology. Our analyses access remote and local data sources in US and Russian waters to characterize oceanographic conditions and analyze the implications of dramatic shifts in recent years. Previously, this region appeared resistant to trends apparent elsewhere in the greater Arctic. Now, the Pacific Arctic also appears to be in rapid transition. The conditions observed in 2017-2019 are unprecedented. We note important shifts in the phenology and magnitude of physical variables, including sea-ice extent, concentration, and duration, as well as extreme reduction in the extent and intensity of the related Bering Sea cold pool. We also note distinct regional dynamics in sea surface temperature in the Bering-Chukchi system, distinguishing western, eastern and northern areas of the Bering Sea. Specifically, our analyses distinguish the northern Bering Sea as an important transition zone between the Pacific and Arctic with higher frequency variability in sea surface temperature anomalies. Our results suggest that the strength and position of the Aleutian Low may be linked to warm to cold phases in the Bering Sea and has an important role in large-scale circulation. While cold winds out of the north are necessary to form ice in the northern Bering Sea, strong winds may be associated with weak sea ice, as wind action may break ice and enhance vertical mixing, counteracting enhanced sea-ice production from the advection of cold air. Research in this important region is complicated by international borders but may be enhanced through international collaboration. This analysis represents an attempt to integrate data across Russian and US waters to more fully represent system-wide processes, to contrast regional trends, and to better understand physical interactions.